Steve, maybe it is a head gasket...that is a lot of pressure loss for a cold engine with no visible leaks. Here's some things to check: listen around the "air" (expansion) area of the surge tank for an air leak rather than a coolant leak; also, check at the water pump shaft and bolts (but you should see coolant coming out there); check to see if your
oil level is overfull, it could be coming up from coolant leaking into the sump (not good); and finally, pull the plugs and crank the motor over to see if coolant has leaked into the chambers.